1. Field of the Invention
The present invention relates to an apparatus for metal coating of bands by electroplating, with a band running through an acidic electrolyte enriched with a metal. The apparatus includes at least one insoluble anode extending parallel to the band and divided, in a running direction of the band, in a plurality of separate anode strips insulated from each other, and means for feeding current to each separate anode strip for precipitating the metal from the electrolyte, with the current flowing from a respective anode strip to the band which forms the cathode.
2. Description of the Prior Art
Usually, the anodes of such apparatuses are wider than a band to be coated in the apparatus. As a rule, for metal coating of the band, only those anode strips are supplied with current which are located either above or below the band. As a result, the anode strips, which are not supplied with current, can be subjected to corrosion. The danger of corrosion is particularly great for the anode strips which are arranged immediately adjacent to the anode strips which are supplied with current and on which both cathode and anode regions are formed. In the cathode regions of the anode strips, which are supplied with current, hydrogen is generated. The hydrogen can penetrate in the anode strips, in particular into the anode strips formed of titanium.
Accordingly, an object of the present invention is to provide, in an apparatus of the type described above, means which would prevent the danger of corrosion of the anode strips, the supply of precipitation current to which is interrupted.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing means for supplying each anode strip with protective current the voltage of which is so selected that the formation of cathode regions on the anode strips, to which the supply of the current for precipitation of metal from the electrolyte is interrupted, is prevented.
The feeding of the protective current prevents the formation of the cathode regions on all of the anode strips. The protective current is so selected that practically no metal precipitation takes place on the anode strips to which the current supply is interrupted, and particularly, no edge growth on the band occur. To meet these requirements, the amount of the protective current is so selected that it constitutes from about 3% to about 10% of the precipitation current.
The protective current supply means can be formed, with small technical expenditures, from current resistors which connect adjacent anode strips. An additional advantage of this very simple solution consists in that even the outer anode strips, which are not supplied with current for precipitating the metal from electrolyte and which are spaced from the last of the anode strips supplied with the precipitation current, are subjected to the action of the protective current. The spacing corresponds to the drop of the voltage gradient. Therefore, the outer anode strips can be exposed to as small as possible protective current.
The novel features of the present invention, which are considered as characteristic of the invention, are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.